None, unless auto focusing in low light is important for you. It is not too good at this.

I can't really add much to all the positive things already said about this lens. It simply blows my other lenses away. Sharpness is amazing, beautiful colours and contrast, great depth of field effects. It is my favourite. You will suddenly expect much better results from your photography but may not get it with the other EF-S lenses. I used this lens constantly for a while after buying it and when I went back to use other lenses they just didn't seem to come up to scratch.